The cardiac cycle has two phases; diastole and systole. During the systolic phase, the heart ejects blood through a pumping action requiring energy. During the diastolic phase, the heart repolarizes electrically, relaxes mechanically and is refilled with blood. In addition, the oxygen needed for the heart to perform its systolic activity is delivered to the heart during diastole. If the diastolic phase is disturbed or shortened in time, the performance during systole is compromised.
In “Diastolic time—frequency relation in the stress echo lab: filling timing and flow at different heart rates”, by Bombardini T. et al., Cardiovascular Ultrasound, 2008 Apr. 21; 6:15, the diastolic and systolic time intervals were studied in normal persons, i.e. persons that do not suffer from cardiac related problems, and in patients suffering from stress induced ischemia and severe mitral regurgitation. The time intervals were measured by means of echocardiography. In particular, the different persons were studied during rest and stress. It was found that, in normal persons, the length of the diastolic time interval approached the length of the systolic time interval during exercise at high heart rates, i.e. heart rates above about 150-160 bpm. For lower heart rates the diastolic time interval was found to be significantly longer than the systolic time interval. Further, during rest, the diastolic time interval was found to be significantly longer than the systolic time interval. On the other hand, for patients suffering from stress induced ischemia and severe mitral regurgitation, the diastolic time interval was found to be substantially equal to, or even shorter than, the systolic time interval at both low and high heart rates.
Thus, the length of the diastolic phase or diastolic time interval of the cardiac cycle seems to be an important parameter which contains valuable information of the cardiac status of a patient. Further, the diastolic time interval and the ratio between the diastolic time interval and the systolic time interval seem to be important and valuable measures for determining a cardiac status of a patient.
There exist a large number of different solutions in which these parameters are utilized for e.g. controlling the functioning of a pacemaker and/or for determining a cardiac status of a patient.
For example, in U.S. Pat. No. 6,792,308 to Corbucci, a cardiac pacemaker for evaluating myocardial performance using information of the diastolic and systolic intervals is disclosed. In particular, the myocardial performance is assessed by determining a QT interval based on electrogram (EGM) readings and by detecting first and second heart sounds (S1 and S2). The QT interval and the timing of the first and second heart sounds is used to evaluate certain parameters related to myocardial performance. Such parameters include a S1S2 interval which is the difference between, on one hand, the interval between the Q-wave and the onset of the first heart sound S1, and, on the other hand, the interval between the Q-wave and the onset of the second heart sound S2. The S1S2 interval serves as an estimate of the systolic interval or the ejection time (ET). Another parameter is the S2S1 interval which is an estimate of the diastolic interval or the filling time (FT). These intervals are used to determine a ratio of the systolic interval to the diastolic interval, which ratio indicates a systolic/diastolic balance. According to U.S. Pat. No. 6,792,308, this ratio is used to evaluate the upper rate limit in paced patients and for evaluating the rate limit for patients with rate dependent angina.
Yet, there is a need within the art of improved medical devices and methods for determining a cardiac status of a patient.